In the event that a casing downhole has a leek, a tube, also called a liner or a clad, having a smaller diameter than the casing is usually placed outside the leak. The liner is then expanded from inside the tube to increase the diameter of the tube to match the diameter of the casing so as to seal the leak in the casing.
A liner is usually made of metal, and usually of the same metal as the casing. When the liner has been expanded to match the diameter of the casing and the expansion tool is retracted from within the liner, the liner will shrink a bit due to the tension in the metal. In this way, the diameter of the liner is somewhat smaller than that of the casing. Therefore, when rolling the liner, the liner is expanded to a larger diameter than the original diameter of the casing. This is obtained by rolling both the liner and the casing to a somewhat larger diameter so that, when the expansion tool is retracted, both the liner and the casing shrink, and the liner is thus able to seal the teak in the casing.
However, expanding the liner into a larger diameter than that of the casing is only possible in the event that the casing can also be expanded. Usually, cement is used to fasten the casing, and the casing is thus surrounded by cement. In this case, the casing cannot be expanded, and rolling the liner will result in a small gap between the outside of the liner and the inside of the casing—and the leak is thus not sealed by the liner.
Known solutions to this problem have been to make a liner of epoxy mixed with fibre glass where the liner is curled, the cross-section of the liner thus being shaped like a flower. In this way, the liner can be uncurled when rolled to abut the inside of the casing, and due to the fact that epoxy does not shrink, the liner will be able to seal the leak as intended.
Another solution to this problem is known from US 2005/057005 in which the liner has projections that, during expansion of the liner, are fastened to the inside of the casing. This is also known from US 2006/0237188. However, these projections may break off, the result being that the liner is released and the leak is not sealed.
In order to insert the liners into the casing or the like, the whole liner needs to have a external diameter greater than that of the casing. When expanding the liner only some of the liner is expanded, e.g. the first part, whereas the second part is not expanded. The result is that the diameter of the casing is decreased in those areas where the liner is not expanded. Thus, the leak in the casing may be sealed, but the fluid flow in the casing or pipeline is substantial decreased making the casing less efficient than before the leak occurred.